Some Pleistocene deposits in North Devon
DOI:
https://doi.org/10.26485/BP/1966/15/11Keywords:
cryogenic processes, solifluction terrace, till, erratic bouldersAbstract
The sequence of Pleistocene deposits which can be seen in the coastal sections around Barnstaple Bay will be described, together with some possible ice-msrginal drainage channels, on the North Devon coast between Lynton and Hartland Quay. The deposits consist mainly of layers of solifluction debris derived by cryergic processes from the underlying bedrock, and these head deposits, as they are called in the English literature, may reach a total thickness of more than 50 feet. The head deposits consist of materiał which has moved down the coastal slope and spread out as a great ''apron" or solifluction terrace, often of wide extent. In general, two distinct layers of head can be detected. There is an upper head (Vistulian/Würm age) which is disturbed in places by frost wedges and convolutions, and which also appears to be less weathered than the lower or main head, regaded as Saale (Riss) in age. No marine beaches transgress the surface of the solifluction terraces.
There is a deposit of calcareous, shelly boulder clay at Fremington, near Barnstaple, and near Fremington Quay and at Middleborough in Croyde Bay, cliff-sections reveal highly weathered remanié deposits of the same till resting upon raised beach shingle, which nearby is sealed below the lower or main head. The boulder clay is regarded as Saale (Riss) in age and to be equivalent to the Irish Sea (Eastern General) till of Southern Ireland.
The raised beach gravels contain erratic boulders, and in places "giant" erratic blocks are known to weigh more than 50 tons each. These "giant" erratics are always sealed below the raised beach or below the main head, and no, boulder clay has been found in close association with them. They are regarded as ice-rafted blocks which have "floated" onto already existing wave-cut platforma in the early Pleistocene. The raised beach gravels are thought to be of Holstein (Mindel-Riss) Interglacial age being sealed by main head and boulder clay of Saale (Riss) age. The last glacistion (Vistulian/Würm) is represented by the comparatively fresh upper head.
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